Abstract: In the densification process of plain weave fabric composite materials, pore defects occur due to imperfect matrix deposition, and interfaces play a role in transmitting loads in plain weave fabric composite materials. Therefore, it is important to establish a damage constitutive model that considers the interface phase and pore defects to describe the mechanical behavior of the material under the influence of interface phase and pore defects, for the design of material structure damage tolerance and selection of interface phase materials. Taking a certain plain weave composite material as the research object, a zero-thickness cohesive damage model and random distributed pore defects were introduced based on the Hashin and maximum stress damage criterion, simulating the microscopic damage initiation and evolution process, and studying the influence mechanism of the plain weave composite material's tensile performance. The study revealed that the incorporation of an interface phase would significantly change the damage distribution of the composite material. When the plain weave composite materials are subjected to force, the interface phases induce cracks to occur at the edge of the model in the direction of the external load, preventing the cracks from directly extending through the fibers, thus changing the damage pattern from being mainly at the fiber bundle lap joints under radial tensile load to being mainly at the unit cell edges; when the porosity rate surpasses a specific range, it will lead to a significant alteration in the damage mode of the composites, and as the porosity rate increased, the material would change from being supported by the fiber bundle, matrix, and interface phase to being supported mainly by the fiber bundle, greatly weakening the material's strength performance. This research outcome provides certain reference basis for the prediction of the strength performance of other composites as well as the study on the influencing mechanism of tensile performance.